Some known implantable lead assemblies that are used with implantable pulse generators (such as neurostimulators, pacemakers, defibrillators, or implantable cardioverter defibrillators (ICD)) are prone to heating and induced current when placed in the strong static, gradient, and/or radiofrequency (RF) magnetic fields of a magnetic resonance imaging (MRI) system. The heating and induced current are the results of the lead assemblies acting as antennas in the magnetic fields generated during a MRI scan. Heating and induced current in the lead assemblies may result in deterioration of stimulation thresholds or, in the context of a cardiac lead, even increase the risk of cardiac tissue damage and perforation.
Many patients with an implantable pulse generator and implanted lead assembly may require, or can benefit from, a MRI scan in the diagnosis or treatment of a medical condition. MRI modality allows for flow visualization, characterization of vulnerable plaque, non-invasive angiography, assessment of ischemia and tissue perfusion, and a host of other applications. The diagnosis and treatment options enhanced by MRI may continue to increase over time. For example, MRI scans have been proposed as a visualization mechanism for lead implantation procedures.
Some known lead assemblies include inductive coils that are electrically coupled to tip electrodes and reduce the induced current within the assemblies when exposed to different external magnetic fields. For example, the lead assemblies may include two coils that are designed to reduce induced current in the electrical path of the tip electrode when the lead assemblies are exposed to different magnetic fields. The coils may be relatively close to each other and to the tip electrode such that the coils may be magnetically coupled. The magnetic coupling of the coils negatively impacts the efficacy of the coils in reducing induced current.
In order to reduce the magnetic coupling of the coils, some known lead assemblies include integrated circuits that are electrically coupled with the coils. The integrated circuits use various techniques to reduce the magnetic coupling between the coils. However, the integrated circuits increase the cost of manufacturing the lead assemblies and increase the size required for the lead assemblies. As a result, the lead assemblies may not be appropriately sized for certain applications, such as the use of the lead assemblies for the treatment of bradycardias. For example, the lead assemblies may be too large and unable to be used as brady leads.